1. Technical Field of the Invention
The invention relates generally to the field of fiber optic networks and systems and more particularly to dispersion compensation in optical and photonic networks.
2. Description of Related Art
The evolution of optical technologies intersecting with the industrial drive to utilize material science in designing an integrated circuit chip as a compact and cost-effective solution creates a platform for an innovative approach in addressing properties associated with optics and electronics. Traditional optical theories provide an understanding to make a purely optical-based device but the resulting product is frequently bulky in size, while electronic theories push relentlessly for a greater integration and miniaturization of integrated circuits by following the so-called Moore's Law. Emerging trends from this phenomenon present a new set of circumstances requiring optical solutions on a small chip that are able to compensate sporadic optical signal variations or perturbations.
A common well-known problem in high-speed transmission of optical signals is chromatic dispersion. Chromatic dispersion refers to the effect in which the various physical wavelengths of an individual optical channel either travel through an optical fiber or component at different speeds—for instance, longer wavelengths travel faster than shorter wavelengths, or vice versa—or else travel different path lengths through a component. This particular problem becomes more acute for data transmission speeds higher than 2.5 gigabits per second (Gbps). The resulting pulses of the signal will be stretched, will possibly overlap, and will cause increased difficulty for optical receivers to distinguish where one pulse begins and another ends. This effect seriously compromises the integrity of a signal. Therefore, for fiber optic communication systems that provide a high transmission capacity, the system must be equipped to compensate for chromatic dispersion.
In FIG. 1, there is shown a conventional single-channel system 100 illustrating the transmission path of an optical signal. The system 100 comprises a transmitter 110 optically connected to a receiver 150 by a dispersion compensation fiber (DCF) 130, an optical amplifier 140, and a single-mode optical fiber (SMF) 120. The DCF 130 is optically connected to the SMF 120 via, for instance, a splice and compensates for chromatic dispersion of an optical signal generated within the SMF 120 for the reason that the DCF 130 possesses dispersion slope characteristics of inverse signs relative to the SMF 120. The transmitter 110 comprises a laser 115 and a modulator 117 that are integrated together on a single chip with the DSF 130 positioned away from the transmitter.
Further, a conventional wavelength division multiplexer (WDM) system 200 for transmitting a plurality of optical channels over a single optical fiber is shown in FIG. 2. The WDM system 200 comprises a plurality of lasers 210, 220, 230 and 240, a plurality of modulators 211, 221, 231 and 241 that are optically coupled to an optical multiplexer (MUX) 250, a single-mode fiber (SMF) 255, a DCF 260, an optical amplifier 270 and a receiver 280. The WDM system 200 processes multiple optical channels represented by wavelengths λ1, λ2, λ3 and λ4 that are generated from the plurality of lasers 210, 220, 230 and 240. In the WDM system 200, the optical MUX 250 combines the four inputs to produce a Wavelength Division Multiplexed composite output optical signal. The multiplexed optical channels together comprise a single composite optical signal that propagates within the SMF 255 and the DCF 260. The DCF 260 is able to compensate for chromatic dispersion for the several channels or wavelengths. The optical amplifier 270 is able to amplify all the channels of the composite optical signal that is delivered to the receiver 280.
In both systems 100 and 200, the physical dimension of the DCF 130 in the system 100 and the DCF 260 in the system 200 is too bulky to fit on a chip. Accordingly, there is a need to design optical systems and methods that solve the dispersion effects functionally but, at the same time, significantly reduce the dimension of a dispersion compensation component for placement on an integrated circuit for operating with a laser-modulator combination.